Abstract:

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The present work deals with the preparation and characterization of ceramic composites
for the substitution of load-bearing bone portions, made of hydroxyapatite (HA) and bioactive β-
calcium silicate (β-Ca2SiO4) as a reinforcing phase. The composite materials were prepared by Fast
Hot-Pressing technique (FHP), which allowed the rapid sintering of monolithic ceramics at
temperatures up to 1500 °C, well above the commonly adopted temperatures for sintering of
hydroxyapatite (1200-1300 °C), in order to achieve the densification of the reinforcing phase also.
XRD analysis reported no formation of secondary phases other than HA and β-Ca2SiO4, after FHP
cycles. Flexural strength tests were performed on selected samples sintered at different
temperatures: the composite materials exhibited increased mechanical resistance compared to
samples constituted of HA only. These preliminary results confirmed that composites of HA and β-
Ca2SiO4 are promising for the development of bioactive load-bearing ceramic bone substitutes.

Abstract: A series of BN-SiO2 composite ceramics with high relative densities have been fabricated by
hot pressing of a mixture of hexagonal boron nitride powder and silica sol. X-ray diffraction (XRD)
results show that silica are distributed in the BN matrix as noncrystalline state. Microstructure of
as-sintered composite ceramics is observed by scanning electron microscopy (SEM). The influence of the
secondary phase on the mechanical properties is studied by varying the silica content from 10 wt% up to
40 wt%. Dielectric properties of composite ceramics are also measured from 1 MHz to 2.0 GHz.

Abstract: High-temperature mechanical properties, machinability, oxidation resistance and thermal shock resistance of different content of carbon particles modified silicon carbide composite ceramics (Cp/SiC) prepared by pressureless sintering techniques were studied. Adhesion of Cp/SiC to melted glass under 1000°C was also observed. The results showed that 15-Cp/SiC had the optimum machinability and it also did not adhere to melted glass at high temperature. And flexural strength, hardness, and fracture toughness of 15-Cp/SiC is 136.5MPa, 274.6kgf/mm2, 2.58MPa•m1/2 respectively. The good performance of Cp/SiC made it possible to be used as high temperature glass fixture, which means that Cp/SiC can not only improve the service life of fixture materials, but also broaden the application fields of SiC ceramics.

Abstract: Hydroxyapatite whisker was the reinforcement phase to prepare whisker/calcium phosphate cement composites, which was obtained by homogeneous precipitation method, with 2.5~15 microns in length, 2~30 length/diameter ratio. Mechanical properties and microstructure of composites were tested. With the increase of hydroxyapatite whisker addition, composites strength reduces after the first rise. When hydroxyapatite whisker is added to 4%(wt), the composite achieves the maximum strength. SEM method was used to observe fracture microstructures of composite materials. As a result, dispersion degree of the HA whisker affects the strength of the material. Too much whiskers can form agglomerates, which weaken composite strength.

Abstract: Silicon nitride nanoceramics were fabricated by hot press sintering two kinds of Si3N4 nano-sized powders. The effect of starting powders on microstructure, mechanical properties and thermal shock resistance were investigated. The microstructure of sintered materials consists of spherical grains and the addition of α–Si3N4 to starting powders does not affect the grain morphology. The flexural strength, fracture toughness and thermal shock resistance increase with the increase in amount of α–Si3N4 starting powders, and the maximum mechanical properties are obtained when the amount of α–Si3N4 powders is 40wt.%. The hardness values decrease with the increase of α–Si3N4 amount.